This proposal aims at designing a cell-therapy based approach to hypopituitarism , with special focus on pituitary dysfunction due to radiation injury. The pituitary gland is a master endocrine organ that orchestrates the function of multiple glands in the organism, under direct control by the hypothalamus. Hypopituitarism is a very prevalent problem following radiation treatment to the brain. It is dose-related, progressive and irreversible; it also contributes to poor quality of life and other substantial problems among cancer survivors. Hypopituitarism is also an important permanent consequence of infection, traumatic brain injury or congenital conditions. We have developed a protocol for the specification of pituitary cells from human ES cells and further differentiation into hormone producing cells. We have also previously optimized a brain radiation model in the rat, using a clinically relevant fractionated radiation course. The animals are well studied for growth, weight and behavioral parameters and we have some preliminary evidence of pituitary dysfunction. Here we propose to optimize the human ES and iPS differentiation protocol to allow the enrichment into specific pituitary cell subtypes. Validation of cell phenotypes is obtained through gene expression and marker profiles, measurements of hormone secretions, as well as in vivo function. Human ES derived pituitary cells are grafted into hypophysectomized nude rats and basal hormone levels are measured in the serum at different time points. Grafts will be placed subcutaneously or orthotopically into the hypothalamus / pituitary interface. We will also graft the cells into the irradiated rats with evidence of pituitary damage. Analysis will focus on revovery of hormone levels in the plasma, as well as evidence of integration of the graft into the hypothalamic - pituitary axis, using stimulation tests. Furthermore, functional analysis will be attempted by asking whetehjr female rats with cell grafts can recover their ability to reproduce and lactate.The proposal addresses a novel problem that has received little attention to date. As we succeed in achieving long term remission among cancer patients, questions of poor quality of life among survivors have acquired a more pressing nature. This project will provide much needed insight into the feasibility of cell based therapy to ameliorate these consequences of brain radiation. It will also undertake the derivation of specific pituitary cell subtypes from humn ES or iPS cells, an unreported achievement in human cells to date.